<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #result {
      width: 200px;
      height: 100px;
      border: 1px solid red;
    }
  </style>
</head>
<body>
  <button id="btn">点击发送请求</button>
  <div id="result"></div>
  <script>
    const div = document.getElementById('result')
    const btn = document.getElementById('btn')
    btn.addEventListener('click', function() {
      const xhr = new XMLHttpRequest()
      // 超时设置 超过两秒就取消请求
      xhr.timeout = 2000
      // xhr.abort() 可以手动取消请求
      // 超时回调
      xhr.ontimeout = function() {
        alert('网络超时，请稍后请求')
      }
      xhr.onerror = function() {
        alert('你的网络出现了一些问题')
      }
      xhr.open('GET', 'http://127.0.0.1:8000/timeout')
      xhr.send()
      xhr.onreadystatechange = function () {
        if (xhr.readyState === 4) {
          if (xhr.status >= 200 && xhr.status < 300) {
            div.innerHTML = xhr.response
          }
        }
      }
    })
  </script>
</body>
</html>